1. Field of the Invention
The invention relates to a fixing method for the blading of a fluid-flow machine and to a fixing arrangement.
2. Brief Description of the Related Art
The fixing of the blading of the above type relates to moving or guide blades inside fluid-flow machines, such as, for example, a compressor or a turbine of a gas turbine plant or another thermal turbomachine. Moving blades are fastened in a fastening slot along the circumference of the rotor of the thermal turbomachine. They are to be positioned in a suitable manner as a function of the respective flow conditions and are to be reliably secured with respect to misalignments which occur or against complete release from the fastening slot during operation of the thermal turbomachine.
There is the risk of individual moving blades being completely released from the circumferential slot if the moving blades are unevenly displaced within the respective fitting clearance in the circumferential direction along the fastening slot on the rotor. Due to such peripheral misalignments, with a multiplicity of moving blades inserted along the fastening slot, a considerable gap may arise between two adjacent moving blades, this gap being large enough for a moving blade to be released from the fastening slot by radial twisting. This may cause considerable damage to the entire turbomachine plant.
Safety measures against the release of individual moving blades from the fastening slot generally relate to the reduction of the clearance between two adjacent blade roots inside the fastening slot. After the fitting of all the moving blades inserted into the fastening slot and of the whole intermediate pieces and the halved intermediate pieces, an “intermediate fitting gap”, into which a “rotor end piece” is inserted, is obtained between two opposite moving blades. This ensures that the clearance present between the moving blades, inserted into the fastening slot, and intermediate pieces is limited to a minimum.
However, on account of the varying thermal expansion behavior between the blades, the rotor end piece and the rotor during operation, a clearance is produced between the blades and the intermediate pieces, located inside the fastening slot, including the rotor end piece. On account of the circumferential clearance arising in the process, a situation may arise in which the end piece halves are displaced relative to one another in such a manner in the circumferential direction along the fastening slot. The intermediate piece may then be released, for example, from the heart-shaped recesses. Such a case leads in turn to the damage scenario already described at the beginning.
In order to prevent such damage, DE-A1-101 34 611 describes a fixing arrangement for blading of a fluid-flow machine in which an intermediate fitting gap is provided between at least two turbine blades inserted in an adjacent position inside the fastening slot. The two insert elements, designed as end piece halves, are inserted into the intermediate fitting gap. These insert elements enclose a gap between them into which a fixing wedge can be inserted. The wedge is characterized by the fact that it provides at least one connecting element toward the side of the turbine blade and at least one of two turbine blades adjoining the wedge provides a mating contour corresponding to the connecting element. Thus the wedge and the turbine blade form a positive-locking connection with one another.
A disadvantage of this embodiment, however, is that additional axial forces are thereby produced, which act on the rotor. These axial forces may lead to the rotor becoming warped, thus causing increased rotor vibrations.